A plasma display panel (hereinafter referred to as a PDP) is basically made of a front panel and a rear panel. The front panel includes: glass substrate; stripe-like display electrodes, each formed of a transparent electrode and bus electrode on one principle surface of the glass substrate; a dielectric glass layer over the display electrodes working as a capacitor; and a protective layer made of magnesium oxide (MgO) formed over the dielectric layer.
The glass substrate is manufactured by the float method, which is used to make a large and flat area. In the display electrodes, a paste containing silver (Ag) to ensure electrical conductivity is applied to the transparent electrodes made by a thin-film forming process, in a predetermined pattern. Then, the pattern is fired to form bus electrodes. A dielectric layer is formed by applying and firing a dielectric paste to cover the display electrodes made of transparent electrodes and bus electrodes. Lastly, a protective layer made of MgO is formed over the dielectric layer using the thin-film forming process.
On the other hand, the rear panel includes: a glass substrate; stripe-like address electrodes formed on one principle surface of the glass substrate; a dielectric layer covering the address electrodes; barrier ribs formed on the dielectric layer; and phosphor layers formed on the dielectric layer between the respective barrier ribs to emit light of red, green, or blue.
The front panel and the rear panel are hermetically sealed with their electrode-forming sides facing to each other. A discharge gas, such as neon(Ne)-xenon(Xe), is filled into a discharge space partitioned by the barrier ribs at a pressure ranging from 400 to 600 Torr. In the PDP, selectively applying an image signal voltage to the display electrodes generates a gas discharge, and ultra-violet rays generated by the discharge excite the respective phosphor layers to emit light of red, green, and blue. “All about plasma display panels” (co-authored by Heiki Uchiike and Shigeo Mikoshiba, published by Kogyo Chosakai Publishing Inc. on May 1, 1997, p. 79-80) discloses an example of displaying color images in such a manner.
A method of dividing one frame of image into a plurality of sub fields (SF) for gradation representation is used to display images. In this method, one SF is divided into an initializing period, addressing period, sustaining period, and erasing period, to control discharge. As a technique of performing stable address discharge during the addressing period for selecting pixels to be lit, Japanese Patent Unexamined Publication Nos. H10-334809, 2003-132801, and 2004-103273 disclose a technique of adding silicon (Si) or aluminum (Al) element to MgO of each protective layer in a concentration ranging from several hundred parts per million to several percents, to improve the electron emission characteristics of the protective layer.
Further, Japanese Patent Unexamined Publication No. 2000-267625 and “The component-specific characteristics and the latest developments of PDPs” (published by JOHOKIKO Co., Ltd. on Mar. 26, 2004, p. 216-218) disclose a technique of changing the discharge waveform during the initializing period into a generally rectangular pulse to have a gradual slope and inhibiting variations in address discharge voltage caused by variations in the shape of each discharge cell or difference in the charged state of the phosphors.
However, recently, there has been growing expectations on image display devices with higher definition, higher gradation, and lower power consumption, such as a high-definition television screen. For full-specification high-definition television screens 24 in. in diagonal that have particularly been expected, the number of pixels is 1920×1125 and the pitch of discharge cells is as small as 0.15 mm×0.48 mm. Such a high-definition PDP poses a problem in that decreases in brightness and efficiency become particularly apparent.
Measures taken to address this problem are to increase the brightness and efficiency by setting the Xe concentration of the discharge gas in the PDP to at least 5%, which is higher than the conventional concentration, or using barrier ribs arranged in a double cross. However, when the Xe concentration of the discharge gas in the PDP is set to at least 5% or barrier ribs arranged in a double cross is used to increase brightness, considerable increases in driving voltage and more unstable address discharge cannot provide high-quality images. When the Xe concentration increases, increases in the amount of Xe ions and MgO more likely to be sputtered shorten the life of the protective layer.
Generally, a method of adding the Si or Al element to MgO to increase electron emission from MgO is employed to address the problem of unstable discharge caused by increases in driving voltage. However, even though this method can make driving voltage slightly smaller in than the case of using a protective layer made of MgO only, the method cannot stabilize address discharge for a high-definition PDP having a relatively long addressing period.
Particularly for a high-definition PDP having an increased Xe concentration of at least 5%, addition of Si or Al to MgO to speed up address scan, stabilize address discharge, and decrease the voltage causes the following problems. When the PDP is attempted to be lit by a method using wall charge on the dielectric layer during the initializing discharge, the driving voltage is lower than that of a PDP using the conventional MgO protective layer. However, excellent characteristics of electron emission from the MgO protective layer even erase the wall charge formed during the initializing period, thus causing lighting failures (addressing failures) and deterioration of image quality.
When a gradually-sloping voltage waveform is used to stabilize address discharge and decrease address voltage, lighting failures (addressing failures) occur more prominently.